The dynamic range of an image is a range of the luminance of the darkest area to the luminance of the brightest area in the image, defined as a ratio between the brightest pixel value and the darkest pixel value. The dynamic range is controlled by adjusting pixel brightness, such as adjusting the luminance of the image. A technique of improving image quality by improving the dynamic range of an image output from an image sensor is called high dynamic range (HDR) imaging.
In HDR imaging, images with different exposure are acquired by capturing the same object two or more times. These images of different exposures are then synthesized into a single output image, thereby increasing the dynamic range with rich gradation of light in the output image. A plurality of images having different exposures may be acquired by differentiating the exposure, i.e. changing the shutter speeds used for the acquisition of the images.
Further, flash lighting may be used in low-illuminance photographing such as photographing at night. When using the flash that may operate in a pre-flash mode, with the intensities of light fixed for the pre-flash and the main flash, a final image may be acquired by using the light emitted from the pre-flash and flash.
Conventionally, when flashes are used for low-illuminance photographing, the amount of light emitted from the flash depends on the light required to illuminate a main object, which may result in a dark background.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.